Well treatment

ABSTRACT

A method for the treatment of a hydrocarbon well comprising administering down the well polymeric particles impregnated with a well treatment chemical or precursor or generator thereof. The particles have a pore volume of at least 20%, and are prepared by a process which comprises preparing an aqueous dispersion of polymer particles containing from 0.05 to 10 times by volume, based on the polymer, of one or more specific first material(s) adding a partly water-soluble second material having a water-solubility of at least ten times that of first material(s) under conditions which prevent or hinder transport of first material(s) through the aqueous phase, whereby second material diffuses into the polymer particles swelled with first material(s) and increases the volume of said particles by from 20 to 1000 times, based on the polymer.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a 371 of PCT/GB01/05087, filed Nov. 19, 2001, thedisclosure of which is incorporated herein by reference.

This invention relates to a method of treating a hydrocarbon well withwell treatment chemicals, in particular by down-hole placement ofpolymeric particles carrying well treatment chemicals or precursors orgenerators thereof, and to such particles and compositions andstructures containing them.

During the operation of a hydrocarbon well (i.e. a gas or oil well)various down-hole problems arise such as corrosion of metal fittings,hydrocarbon flow-inhibiting deposition (e.g. of scale, gas clathrates,metal sulphides, waxes, gel polymers, microbial debris, etc.),generation of toxic hydrogen sulphide by sulphate-reducing bacteria,increased water flow into the producer bore, etc.

Thus, for example, where sea water is injected through an injection borehole into an oil-bearing stratum to drive oil through the formation(i.e. the rock) into the producer well hole, differences in solutes inthe injection water and the water already present in the formation cancause metal salts to precipitate as scale so causing graduallyincreasing clogging of the producer well hole.

Typically this is dealt with by applying a “squeeze” of scale inhibitorchemicals, i.e. chemicals which break down the scale and increase oil orgas flow. This generally involves ceasing hydrocarbon flow, forcing anaqueous solution of the scale inhibitor down the producer bore underpressure to drive the inhibitor solution into the formation, andrestarting production. Such treatment generally allows a further six orso months of hydrocarbon flow before a further squeeze is required andeach squeeze causes some damage to the formation surrounding theproducer bore hole and as a result an increased flow of formationfragments (i.e. rock grains etc.) into the bore.

The producer bore hole in an oil well is generally lined in thehydrocarbon bearing stratum with “gravel packs”, sand containing filterelements, which serve to trap formation fragments and it has beenproposed to include in such gravel packs ceramic particles coated withor impregnated with well treatment chemicals such as scale inhibitors(see EP-A-656459 and WO 96/27070) or bacteria (see WO 99/36667).Likewise treatment of the formation surrounding the producer well borehole with well treatment chemicals before hydrocarbon production beginshas also been proposed, e.g. in GB-A-2290096 and WO 99/54592.

Various polymeric, oligomeric, inorganic and other particulate carriersfor well treatment chemicals are also known, e.g. ion exchange resinparticles (see U.S. Pat. No. 4,787,455), acrylamide polymer particles(see EP-A193369), gelatin capsules (see U.S. Pat. No. 3,676,363),oligomeric matrices and capsules (see U.S. Pat. No. 4,986,353 and U.S.Pat. No. 4,986,354), ceramic particles (see WO 99/54592, WO 96/27070 andEP-A-656459), and particles of the well treatment chemical itself (seeWO 97/45625).

There is still a need for means of well treatment which give a prolongedperiod of protection, e.g. against scale or other problems, such ascorrosion or hydrocarbon flow restricting problems.

We have now found that polymeric particles produced by theswell-polymerization technique developed by the late Professor JohnUgelstad are especially suitable as carriers for well treatmentchemicals and their precursors in view of their high porosity andsubstantial monodispersity. Such particles may be produced as describedin EP-B-3905, U.S. Pat. No. 4,530,956 and WO 99/19375 the contents ofwhich are hereby incorporated by reference and are referred to herein asmonodisperse polymer particles or MPP.

Thus viewed from one aspect the invention provides a method for thetreatment of a hydrocarbon well which method comprises administeringdown said well polymeric particles impregnated with a well treatmentchemical or precursor or generator thereof, said particles having a porevolume of at least 20%, preferably at least 30%, and being prepared by aprocess which comprises preparing in a first step an aqueous dispersionof polymer particles containing from 0.05 to 10 times by volume, basedon the polymer, of one or more materials having a water-solubility of<10⁻² g/l and having a molecular weight of <5000 g/mol (herein referredto as Substance I) said Substance I not being an oligomer of the polymerforming the particles and being non-crystalline at the temperature atwhich it is incorporated into the particles and is in liquid form at thetemperature at which Substance II is introduced in a second step, and insaid second step adding a partly water-soluble material (herein referredto as Substance II) having a water-solubility of at least ten times thatof Substance I under conditions which prevent or hinder transport ofSubstance I through the aqueous phase, whereby Substance II diffusesinto the polymer particles swelled with Substance I and increases thevolume of said particles by from 20 to 1000 times, based on the polymer.

The polymer particles used may be particles prepared by theswell-polymerisation process (i.e. according to EP-B-3905) or may beparticles prepared from seed particles produced by such a process andthen further enlarged, e.g. as described in WO 99/19375. For furtherdiscussions of “Substance I” and “Substance III”, the reader is referredto EP-B-3905.

Viewed from a further aspect the invention provides polymeric particlesimpregnated with a well treatment chemical or precursor or generatorthereof, said particles having a pore volume of at least 20%, preferablyat least 30%, and being prepared by a process which comprises preparingin a first step an aqueous dispersion of polymer particles containingfrom 0.05 to 10 times by volume, based on the polymer, of one or morematerials having a water-solubility of <10⁻² g/l and having a molecularweight of <5000 g/mol (herein referred to as Substance I) said SubstanceI not being an oligomer of the polymer forming the particles and beingnon-crystalline at the temperature at which it is incorporated into theparticles and is in liquid form at the temperature at which Substance IIis introduced in a second step, and in said second step adding a partlywater-soluble material (herein referred to as Substance II) having awater-solubility of at least ten times that of Substance I underconditions which prevent or hinder transport of Substance I through theaqueous phase, whereby Substance II diffuses into the polymer particlesswelled with Substance I and increases the volume of said particles byfrom 20 to 1000 times, based on the polymer.

Viewed from another aspect the invention provides the use for themanufacture of hydrocarbon well treatment compositions of polymericparticles impregnated with a well treatment chemical or precursor orgenerator thereof, said particles having a pore volume of at least 20%,preferably at least 30%, and being prepared by a process which comprisespreparing in a first step an aqueous dispersion of polymer particlescontaining from 0.05 to 10 times by volume, based on the polymer, of oneor more materials having a water-solubility of <10⁻² g/l and having amolecular weight of <5000 g/mol (herein referred to as Substance I) saidSubstance I not being an oligomer of the polymer forming the particlesand being non-crystalline at the temperature at which it is incorporatedinto the particles and is in liquid form at the temperature at whichSubstance II is introduced in a second step, and in said second stepadding a partly water-soluble material (herein referred to as SubstanceII) having a water-solubility of at least ten times that of Substance Iunder conditions which prevent or hinder transport of Substance Ithrough the aqueous phase, whereby Substance II diffuses into thepolymer particles swelled with Substance I and increases the volume ofsaid particles by from 20 to 1000 times, based on the polymer.

Viewed from a still further aspect the invention comprises a hydrocarbonwell treatment composition comprising a carrier liquid containingpolymeric particles impregnated with a well treatment chemical orprecursor or generator thereof, said particles having a pore volume ofat least 20%, preferably at least 30%, and being prepared by a processwhich comprises preparing in a first step an aqueous dispersion ofpolymer particles containing from 0.05 to 10 times by volume, based onthe polymer, of one or more materials having a water-solubility of <10⁻²g/l and having a molecular weight of <5000 g/mol (herein referred to asSubstance I) said Substance I not being an oligomer of the polymerforming the particles and being non-crystalline at the temperature atwhich it is incorporated into the particles and is in liquid form at thetemperature at which Substance II is introduced in a second step, and insaid second step adding a partly water-soluble material (herein referredto as Substance II) having a water-solubility of at least ten times thatof Substance I under conditions which prevent or hinder transport ofSubstance I through the aqueous phase, whereby Substance II diffusesinto the polymer particles swelled with Substance I and increases thevolume of said particles by from 20 to 1000 times, based on the polymer.

Viewed from a yet further aspect the invention comprises a tubularfilter for down-hole placement containing polymeric particlesimpregnated with a well treatment chemical or precursor or generatorthereof, said particles having a pore volume of at least 20%, preferablyat least 30%, and being prepared by a process which comprises preparingin a first step an aqueous dispersion of polymer particles containingfrom 0.05 to 10 times by volume, based on the polymer, of one or morematerials having a water-solubility of <10⁻² g/l and having a molecularweight of <5000 g/mol (herein referred to as Substance I) said SubstanceI not being an oligomer of the polymer forming the particles and beingnon-crystalline at the temperature at which it is incorporated into theparticles and is in liquid form at the temperature at which Substance IIis introduced in a second step, and in said second step adding a partlywater-soluble material (herein referred to as Substance II) having awater-solubility of at least ten times that of Substance I underconditions which prevent or hinder transport of Substance I through theaqueous phase, whereby Substance II diffuses into the polymer particlesswelled with Substance I and increases the volume of said particles byfrom 20 to 1000 times, based on the polymer.

In the method of the invention the impregnated polymer particles may beplaced down hole before and/or after hydrocarbon production (i.e.extraction of oil or gas from the well) has begun. Preferably theimpregnated particles are placed down hole before production has begun,especially in the completion phase of well construction.

The impregnated particles may be placed within the bore hole (e.g. inthe hydrocarbon bearing strata or in ratholes) or within the surroundingformation (e.g. in fissures or within the rock itself). In the formercase, the particles are conveniently contained within a tubular filter,e.g. a gravel pack or a filter structure as disclosed in EP-A-656459 orWO 96/27070; in the latter case, the impregnated particles arepreferably positioned by squeezing a liquid composition containing theparticles down the bore hole. Preferably, before production begins theimpregnated particles are placed both within the bore in a filter andwithin the surrounding formation.

Where the impregnated particles are placed within the surroundingformation, the pressure used should be sufficient to cause the particlesto penetrate at least lm, more preferably at least 1.5 m, still morepreferably at least 2 m, into the formation. If desired, the impregnatedparticles may be applied in conjunction with proppant particles (e.g. asdescribed in WO 99/54592) to achieve a penetration of up to about 100 minto the formation. Compositions comprising proppant particles andimpregnated polymer particles according to the invention form a furtheraspect of the invention.

The impregnated particles according to the invention advantageously havemode particle sizes (e.g. as measured with a Coulter particle sizeanalyser) of 1 μm to 5 mm, more preferably 10 μm to 1000 μm, especially250 to 800 μm. For placement within the formation, the mode particlesize is preferably 1 to 50 μm, especially 2 to 20 μm. For any particularformation, formation permeability (which correlates to the pore throatsizes in the formation) may readily be determined using rock samplestaken during drilling and the optimum impregnated particle size may thusbe determined. Since the “Ugelstad” particles have a very low dispersity(i.e. size variation), a highly uniform deposition and deep penetrationinto the formation can be achieved. For this reason, the particlespreferably have a coefficient of variation (CV) of less than 10%, morepreferably less than 5%, still more preferably less than 2%.

CV is determined in percentage as

${C\; V} = {100 \times \frac{{standare}\mspace{14mu}{deviation}}{mean}}$where mean is the mean particle diameter and standard deviation is thestandard deviation in particle size. CV is preferably calculated on themain mode, i.e. by fitting a monomodal distribution curve to thedetected particle size distribution. Thus some particles below or abovemode size may be discounted in the calculation which may for example bebased on about 90% of total particle number (of detectable particlesthat is). Such a determination of CV is performable on a Coulter LS 130particle size analyzer.

For placement in filters, the impregnated particles preferably have modeparticle sizes of 50 to 5000 μm, more especially 50 to 1000 μm, stillmore preferably 100 to 500 μm. In such filters, the impregnatedparticles preferably constitute 1 to 99% wt, more preferably 2 to 30%wt, still more preferably 5 to 20% wt of the particulate filter matrix,the remaining matrix comprising particulate oil- and water-insolubleinorganic material, preferably an inorganic oxide such as silica,alumina or alumina-silica. Particularly preferably, the inorganic oxidehas a mode particle size which is similar to that of the impregnatedpolymer particles, e.g. within 20%, more preferably within 10%. As withthe in-formation placement, the impregnated polymer particles preferablyhave low dispersity, e.g. a CV of less than 10%, more preferably lessthan 5%, still more preferably less than 2%. The low dispersity servesto hinder clogging of the filters.

The monodisperse polymer particles preferably have pore size radii of 10to 30000 Å, more preferably 50 to 10000 Å, especially 100 to 5000 Å.Advantageously particles are used having a range of pore size radii sothat materials contained therein have a range of leaching rates.

Unlike the prior art inorganic particulate carriers, capsule carriersand oligomeric carriers for well treatment chemicals, the Ugelstadparticles can be made with very high porosity, allowing the particles tobe uniformly impregnated with a large quantity of the well treatmentchemical which will leach out over a prolonged period and yet leavestructurally intact particles. Accordingly, the impregnated particlesare preferably particles having a pore volume of at least 25%, morepreferably at least 30%, e.g up to 90%.

The particles used according to the invention, eg. MPP or otherstep-grown polymer particles, are preferably vinyl homo- and copolymersmore preferably styrenic homo- and copolymers. Examples of appropriatemonomers include vinyl aliphatic monomers such as esters of acrylic andmethacrylic acids, acrylonitrile, and vinyl aromatic monomers such asstyrene and substituted styrenes. Preferred polymers are styrenicpolymers, optionally and preferably cross-linked, e.g. with divinylbenzene, and particles of such polymers are commercially available in arange of sizes and pore volumes from Dyno Specialty Polymers AS ofLillestrøm, Norway. If desired, the particles may be functionalised,e.g. to provide surface acidic or basic groups (e.g. carboxyl or aminofunctions), for example to scavenge metal atoms from water reaching theparticles so as to reduce scale formation, to promote particle adhesionto formation surfaces, to promote or hinder particle aggregation, etc.Again functionalised particles are available from Dyno SpecialtyPolymers AS.

Preferably the polymer matrix of the impregnated particles has asoftening point above the temperatures encduntered down hole, e.g. oneabove 70° C., more preferably above 100° C., still more preferably above150° C.

The well treatment chemicals or precursors or generators thereof withwhich the MPP are impregnated may be any agents capable of tackling downhole problems, such as corrosion, hydrocarbon flow reduction, or H₂Sgeneration. Examples of such agents include scale inhibitors, foamers,corrosion inhibitors, biocides, surfactants, oxygen scavengers, bacteriaetc.

The material with which the MPP are impregnated may be a well treatmentchemical itself or a precursor chemical compound which in situ willreact, e.g. break down, to produce a well treatment chemical, oralternatively it may be a biological agent, e.g. an enzyme or bacteriumwhich produces a well treatment chemical which exerts its effect withinor outside the bacterial cells.

In general, the well treatment chemicals will be oil-insoluble andwater-soluble chemicals which leach out of the impregnated particleswhen water begins to reach the bore hole or the area of the formation inwhich the particles are placed. Where the particles are impregnated withwell treatment chemical generating bacteria, these are preferablythermophilic bacteria which in the absence of water are in a dormantphase, and especially preferably they are ultra microbacteria ornanobacteria. Generally where the particles are impregnated withbacteria, they will also be impregnated with nutrients for the bacteria,e.g. sucrose, so that bacterial growth is promoted once the particlesencounter water.

Example of typical well treatment chemicals, precursors and generatorsare mentioned in the patent publications mentioned herein, the contentsof all of which are hereby incorporated by reference.

Thus for example typical scale inhibitors include inorganic and organicphosphonates (e.g. sodium aminotrismethylenephosphonate),polyaminocarboxylic acids, polyacrylamines, polycarboxylic acids,polysulphonic acids, phosphate esters, inorganic phosphates, polyacrylicacids, insulins (e.g. sodium carboxymethyl insulin), phytic acid andderivatives (especially carboxylic derivatives) thereof, polyaspartates,etc.

The use of environmentally friendly scale inhibitors, e.g. insulins,phytic acid and derivatives thereof and polyaspartates, is especiallypreferred. It is also novel and the use of such chemicals as down-holescale inhibitors forms a further aspect of the present invention.

Where the scale inhibitor is a polymer it may of course contain residuesof one or more different comonomers.

Examples of preferred well treatment chemicals include: hydrateinhibitors, scale inhibitors, asphaltene inhibitors, wax inhibitors andcorrosion inhibitors. Such inhibitors are well known to those working inthe field of well treatment.

Where the impregnated particles are placed within the formation, theyare preferably applied as a dispersion in a liquid carrier. For pre- andpost-completion application, the liquid carrier preferably comprises anon-aqueous organic liquid, e.g. a hydrocarbon or hydrocarbon mixture,typically a C₃ to C₁₅ hydrocarbon, or oil, e.g. crude oil. For curativetreatment, i.e. after production has continued for some time, the liquidcarrier may be aqueous or non-aqueous.

Impregnation of the well treatment chemical, precursor or generator intothe MPP may be effected by any conventional manner, e.g. by contactingthe particles with an aqueous or non-aqueous solution or dispersion ofthe chemical, precursor or generator followed if necessary by solventremoval, e.g. by draining, drying or under vacuum.

However it is especially preferred to impregnate the particles by slurrymixing, i.e. by adding a quantity of solution which is close to the porevolume of the particles, e.g. 0.8 to 1.2 times pore volume morepreferably 0.9 to 1.1 times pore volume. Still more preferred is toimpregnate the particles by spraying a solution onto a fluidized bed ofthe particles, for example a gas flow fluidized bed or more preferably amechanically fluidized bed, e.g. one fluidized using a Forberg mixer. Ifdesired particle loading may be increased by carrying out more than oneimpregnation step.

The invention will now be described further with reference to thefollowing non-limiting Examples:

EXAMPLE 1

Beads Impregnated with Insulin

5 g of styrene:divinyl benzene polymer particles (pore volume 40%, 100μm particle diameter, available from Dyno Speciality Polymers AS,Lillestrøm, Norway) were placed in a 250 mL round flask for a rotovapor.The flask was evacuated to a pressure of 2 mbar with moderate rotation.After 10 minutes, a mixture of 25 g of a 10% wt aqueous solution ofsodium carboxymethyl insulin (Carbocyline CM 10PP from Cosun IndustrialInsulin Derivatives, Netherlands) and 25 mL methanol was added. Theflask was rotated for one hour at ambient temperature under reducedpressure. The flask was removed from the rotator, 60 mL of n-butylacetate was added and the flask was placed in a warming blanket.

The flask was mounted with a water-separator with a water cooler andheated to reflux (about 90° C.), removing about 25 mL of water. Theparticles were then filtered and dried under vacuum at 40° C.

EXAMPLE 2

Beads Impregnated with Insulin

3 g of styrene:divinyl benzene polymer particles (as used for Example 1)were dispersed in a mixture of 15 g of a 10% wt aqueous solution ofsodium carboxymethyl insulin and 15 mL of methanol in a 250 mL roundflask. The flask was evacuated to 2 mbar and heated to 50° C. androtated at moderate speed until the particles were dry.

EXAMPLE 3

Beads Impregnated with Pentaphosphonate

3 g of 112 μm porous polymer particles (T-12—available from DynoSpeciality Polymers AS) were dispersed in 12 g of an aqueouspentaphosphonate solution (Champion SA 1130) in a 250 mL round flask fora rotavapor. Sodium hydrogen carbonate was then added so as to form thesodium salt of the pentaphosphonate. Addition continued until carbondioxide generation ceased. The pH of the mixture was then determined tobe about 7.

The flask was evacuated to 5 to 10 mbar on a rotovapor and then rotatedslowly at ambient temperature for 30 minutes. The evacuation removed anyremaining carbon dioxide. The flask was then rotated at 40° C. until allthe water was distilled off. 9.6 g of dry crude product was obtained. 3g was removed and the remainder was rinsed with 50 mL water which wasthen separated off by filtration. The rinsed particles were then driedat 40-50° C. yielding 2.19 g of dried impregnated particles.

EXAMPLE 4

Beads Impregnated with Insulin

3 g of 112 μm porous polymer particles (T-12—available from DynoSpeciality Polymers AS) and 13.5 g insulin were placed in a 250 mL roundflask for a rotovapor and 25 mL of water was added.

The flask was evacuated to 5 to 10 mbar on a rotovapor and then rotatedslowly at ambient temperatures for 30 minutes. It was then rotated at40° C. until all the water had been distilled off. 8.5 g of dry crudeproduct was obtained. 3 g was removed, and the remainder was rinsed byaddition of water (25 mL) which was then removed by filtrationwhereafter the particles were dried at 40-50° C. 1.75 g of insulinloaded particles were obtained after this drying.

1. A method for the treatment of a hydrocarbon well, which methodcomprises administering, down said well, polymeric particles impregnatedwith a well treatment chemical or precursor or generator thereof,wherein said particles have a pore volume of at least 20%, and areprepared by a process which comprises: (A) preparing an aqueousdispersion of polymer particles containing from 0.05 to 10 times byvolume, based on the polymer, of one or more first material(s) having awater-solubility of <10⁻² g/l and having a molecular weight of <5000g/mol, said first material(s) not being an oligomer of the polymerforming the particles and being non-crystalline at the temperature atwhich it is incorporated into the particles and is in liquid form at thetemperature at which a partly water-soluble material is introduced instep (B); and (B) adding a partly water soluble second material, havinga water-solubility of at least ten times that of said first material(s),under conditions which prevent or hinder transport of said firstmaterial(s) through the aqueous phase, whereby said second materialdiffuses into the polymer particles swelled with said first material(s)and increases the volume of said particles by from 20 to 1000 times,based on the polymer.
 2. The method as claimed in claim 1, wherein saidpolymeric particles are administered down said well before hydrocarbonproduction from said well begins.
 3. The method as claimed in claims 1or 2, wherein said polymeric particles are placed in a filter in thebore-hole of said well and within the formation surrounding saidbore-hole.
 4. The method as claimed in claim 1, wherein said welltreatment chemical or precursor or generator thereof is selected fromthe group consisting of a scale inhibitor, corrosion inhibitor, waxinhibitor, asphaltene inhibitor, foamer, biocide, surfactant, oxygenscavenger and bacteria.
 5. Polymeric particles impregnated with a welltreatment chemical or precursor or generator thereof, wherein saidparticles are prepared by a process which comprises: (A) preparing anaqueous dispersion of polymer particles containing from 0.05 to 10 timesby volume, based on the polymer, of one or more first material(s) havinga water-solubility of <10⁻² g/l and having a molecular weight of <5000g/mol, said first material(s) not being an oligomer of the polymerforming the particles and being non-crystalline at the temperature atwhich it is incorporated into the particles and is in liquid form at thetemperature at which a partly water-soluble material is introduced instep (B); (B) adding to said aqueous dispersion obtained in step (A), apartly water soluble second material, having a water-solubility of atleast ten times that of said first material(s), under conditions whichprevent or hinder transport of said first material(s) through theaqueous phase, whereby said second material diffuses into the polymerparticles swelled with said first material(s) and increases the volumeof said particles by from 20 to 1000 times, based on the polymer; and(C) contacting said particles obtained in step (B) with an aqueous ornon-aqueous solution or dispersion of said chemical, precursor orgenerator thereof, and said particles have a pore volume of at least20%, wherein said well treatment chemical or precursor or generatorthereof is a scale inhibitor selected from the group consisting of aninsulin, phytic acid, phytic acid derivative and polyaspartate.
 6. Ahydrocarbon well treatment composition comprising a carrier liquidcontaining polymeric particles impregnated with a well treatmentchemical or precursor or generator thereof, wherein said particles havea pore volume of at least 20%, and are prepared by a process whichcomprises: (A) preparing an aqueous dispersion of polymer particlescontaining from 0.05 to 10 times by volume, based on the polymer, of oneor more first material(s) having a water-solubility of <10 ⁻² g/l andhaving a molecular weight of <5000 g/mol, said first material(s) notbeing an oligomer of the polymer forming the particles and beingnon-crystalline at the temperature at which it is incorporated into theparticles and is in liquid form at the temperature at which a partlywater-soluble material is introduced in step (B); (B) adding to saidaqueous dispersion obtained in step (A), a partly water soluble secondmaterial, having a water-solubility of at least ten times that of saidfirst material(s), under conditions which prevent or hinder transport ofsaid first material(s) through the aqueous phase, whereby said secondmaterial diffuses into the polymer particles swelled with said firstmaterial(s) and increases the volume of said particles by from 20 to1000 times, based on the polymer; and (C) contacting said particlesobtained in step (B) with an aqueous or non-aqueous solution ordispersion of said chemical, precursor or generator thereof, whereinsaid well treatment chemical or precursor or generator thereof is ascale inhibitor selected from the group consisting of an insulin, phyticacid, phytic acid derivative and polyaspartate.
 7. A tubular filter fordown-hole placement containing polymeric particles impregnated with awell treatment chemical or precursor or generator thereof, wherein saidparticles have a pore volume of at least 20%, and are prepared by aprocess which comprises: (A) preparing an aqueous dispersion of polymerparticles containing from 0.05 to 10 times by volume, based on thepolymer, of one or more first material(s) having a water-solubility of<10⁻² g/l and having a molecular weight of <5000 g/mol, said firstmaterial(s) not being an oligomer of the polymer forming the particlesand being non-crystalline at the temperature at which it is incorporatedinto the particles and is in liquid form at the temperature at which apartly water-soluble material is introduced in step (B); and (B) addingto said aqueous dispersion obtained in step (A), a partly water solublesecond material, having a water-solubility of at least ten times that ofsaid first material(s), under conditions which prevent or hindertransport of said first material(s) through the aqueous phase, wherebysaid second material diffuses into the polymer particles swelled withsaid first material(s) and increases the volume of said particles byfrom 20 to 1000 times, based on the polymer.
 8. The filter as claimed inclaim 7, wherein said filter comprises a particulate filter matrix ofwhich said polymeric particles constitute 2 to 30% wt.
 9. The filter asclaimed in claim 7 or 8, wherein said well treatment chemical orprecursor or generator thereof is selected from the group consisting ofa scale inhibitor, corrosion inhibitor, wax inhibitor, asphalteneinhibitor, foamer, biocide, surfactant, oxygen scavenger and bacteria.10. The method as claimed in claim 4, wherein said particles areimpregnated with a scale inhibitor selected from the group consisting ofinsulin, phytic acid, phytic acid derivative and polyaspartate.